A. The invertible matrices
B. The matrices whose entries are all integers
C. The symmetric matrices
D. The matrices whose entries are all greater than or equal to
E. The matrices with all zeros in the third row
F. The diagonal matrices

Wouldn't it be all because they're all subsets of R^(3x3) ??

Could someone kindly explain to me how to find the answers, and what the answer would be to that question?

This question has to do with linear dependency:
Which of the following sets of vectors are linearly independent?